CC Mode. Allow fontification of "wrong" style comments with warning face.

This fixes bug #4192.

* etc/NEWS: Add a new entry.

* lisp/progmodes/cc-defs.el (c-font-lock-flush): New macro.

* lisp/progmodes/cc-cmds.el (c-toggle-comment-style): On toggling the comment
style, invoke c-font-lock-flush when c-mark-wrong-style-of-comment is non-nil,
to cause that marking to be done instead on the other style of comment.

* lisp/progmodes/cc-fonts.el (c-maybe-font-lock-wrong-style-comments): New
function.
(c-cpp-matchers): Call c-maybe-font-lock-wrong-style-comments when
appropriate.

* lisp/progmodes/cc-vars.el (c-mark-wrong-style-of-comment): New customizable
option.

* doc/misc/cc-mode.texi (top level, Indentation Commands, Guessing the Style,
Custom Macros): For some opening quote marks, correct '' to ``.
(Minor Modes): Add an xref to the new page "Wrong Comment Style" in a
footnote.
(Wrong Comment Style): New page.

1 files changed, 8 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 95d6b9b5bd4..61b9f933f15 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -2264,6 +2264,14 @@ file-local variable, you may need to update the value.
 *** Declare 'define-overload' and 'define-child-mode' as obsolete
 *** Rename several internal functions to use a ''mode-local-' prefix
 
+** CC Mode
+
++++
+*** You can now flag "wrong style" comments with font-lock-warning-face.
+To do this, use c-toggle-comment-style, if needed, to set the desired
+default comment style (block or line); then set the option
+c-mark-wrong-style-of-comment to non-nil.
+
 
 * New Modes and Packages in Emacs 27.1